Parallel Sorting - PowerPoint PPT Presentation

Parallel Sorting. Sort. Sorting operation is frequently used for database processing. For example sorting may be requested by users through the use of Distinct, Order By and Group By clauses in SQL.

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Partition Phase: each PN first scans its local tuples and distributes them as buckets according to range partitioning.

Optimization Phase: a coordinator PN is used to monitor the load for every PN. If every PN has the similar amount of data to process, Go to Sorting Phase. Otherwise, the imbalanced work load is detected, thus, a redistributed partitioning is needed.

Phase 1. Bucket Sizes Counting : Each PN reads its local data and computes each bucket size according to range distribution. Thereafter, each PN transfers the bucket information to a coordinator.

Phase 2. Load Balancing Optimization: coordinator decides the distribution strategy for assigning each bucket to PNs according to their bucket IDs sequentially. Whether coordinator assigns one more next bucket (size B) to current PNi will be decided on: if (Pi+B)-Pavg< d, it will assign next bucket to PNi. Otherwise, the bucket will be assigned to next PNi+1. This phase only decides the distribution strategy without any data transferred.

Phase 2. Load Balancing Optimization with Fragment Feature : coordinator decides the distribution strategy for assigning each bucket to PNs according to their bucket IDs sequentially. Suppose that the next bucket (size B andPi+B>Pavg), with the interval of data values from rs to re ( rs < re ), is being considered for the assignment. The coordinator will fragment this bucket into two portions. Suppose that PNi already has total size Piof tuples which is d tuples less than Pavg (Pi+d=Pavg). The first portion which consists of those data values within the range of rs to rs+(re-rs)d/B of the bucket will be assigned to current PNi. The second portion which consists of the remaining data of the bucket will be assigned to next PNi+1. Again, this phase is without any data transferred.